Extending the π-Conjugated System in Conjugated Microporous Polymers to Modulate Excitonic Effects for Metal-Free Selective CO<sub>2</sub> Photoreduction to CH<sub>4</sub>
Meng Fanyu, Juan Wang, Minghui Chen, Zhenguang Wang, Guoyi Bai, Xingwang Lan
Abstract
Photocatalytic CO 2 reduction into CH 4 is an appealing approach to alleviate the current energy and environmental crisis; however, achieving high selectivity and conversion efficiency still remains challenging. The rational design of photocatalysts for CO 2 adsorption and activation is thus crucial. Here, we designed and synthesized two redox-active truxene-based conjugated microporous polymers linked by thiazolo[5,4- d ]thiazole for metal-free photocatalytic reduction of CO 2 to CH 4 . Significantly, the optimized polymer with the extended π-conjugated system, denoted Tx-TzTz-CMP-2, presented a higher CH 4 production rate of 300.6 μmol g –1 h –1 with a selectivity of 71.2% without any metal cocatalyst and photosensitizer, which outperformed most of the previously reported photocatalysts. Experimental and theoretical investigations revealed that introducing phenyl as a π-bridge extending electron delocalization of conjugated system might effectively minimize exciton binding energy, thereby boosting the intramolecular charge transfer and separation abilities. Meanwhile, the N-site of the thiazole unit acted as an electron reservoir and a catalytic center for activating the adsorbed CO 2 and forming CH 4 by subsequent hydrogenation. This work highlights the significance of the extended π-conjugated system in metal-free conjugated microporous polymers to improve the activity and selectivity of CO 2 photoreduction to CH 4 .